Near-sightedness, also known as short-sightedness or myopia, is a condition of the eye where light undesirably focuses in front of, instead of on, the retina. The improper positioning of the light focus has undesirable vision consequences, as distant objects appear blurry while close objects appear more normal. Experiencing blurry images can manifest as headaches and eye strain. It is known for severe near-sightedness, increase in risk of retinal detachment, cataracts, and glaucoma can be experienced by the person. The underlying mechanism of myopia involves the length of the eyeball being too long or less commonly the lens being too strong, and as such can be characterized as a type of refractive error.
Myopia can be corrected with eyeglasses, contact lenses, or surgery, however such correction is short-lived as the degree of myopia for a person's eyeball can increase over time, thus requiring changes to their prescription eyeglasses and contact lenses. As surgery does not prevent the progression of myopia, additional surgeries may be required if myopia continues to develop. As such, eyeglasses are the easiest and safest method of correction, eyeglasses are only a temporary corrective measure and therefore do not provide for myopia control, i.e. inhibiting the progression of myopia (e.g. continual lengthening of the person's eyeball over time). Contact lenses can provide for myopia control (to some degrees depending on the design of the lens) as well for myopia correction. The chance of myopia control may be limited with various degree of success depending on the formats used. However, all kinds of contact lenses may associate with a risk of infection due to close contact with the corneal surface during application, which causes abrasion and scratching of the cornea eyeball. A properly designed lens may reduce these risks. Refractive surgery can permanently change the shape of the cornea; however this type of correction suffers the same disadvantages as eyeglasses when it comes to the lack of effective myopia control. Orthokeratology or overnight corneal reshaping uses the forces created under specially designed reverse geometry GP (gas permeable) lenses, or molds, to temporarily change corneal shape for myopia reduction (correction). Normal vision can be achieved during the entire day with long term myopia controlling effect.
In terms of contact lenses for myopia control, a treatment zone (of the contact lens) applies suction to the eyeball in order to reform the eyeball shape and thus decrease the length of the eyeball. However, the treatment zone needs to have an increased strength for higher levels of myopia, however this also causes a disadvantage of the suction force being too great and thus causes the contact lens to contact the surface of the eyeball and become stuck or otherwise attached thereon. In extreme examples, it has been observed that a high myopia lens creates an audible popping sound when removed from the eyeball, clear evidence of lens adhesion to the eyeball surface. Contact with the eyeball needs to be avoided, as this contact contributes to abrasion of the eyeball surface tissues as the lens moves about the eyeball during eye movement (e.g. during REM—rapid eye movement), as well as when the lens is applied or removed with respect to the eyeball. Known examples of lens types applied to myopia for orthokeratology are spherical and toric, however both of these lens types suffer from the disadvantage stated above for higher levels of myopia, i.e. increased risk and occurrence of lens adhesion to the eyeball surface. Current state for the art for myopia lenses dictates that increasing suction levels are accomplished via decreasing the width of the fitting zone, however decreased widths cannot accommodate for manufacturing tolerances/errors of the lens material as well as ability for the eyeball tissue to react (i.e. deform) properly to the applied suction forces. On the contrary, increased widths of the fitting zone can provide room for the eyeball tissue to react properly to the applied suction forces, as well as to inhibit manufacturing tolerances/errors of the lens material. However increasing the fitting zone width has the undesirable consequence of reducing the strength of the suction force and thus making the lens ineffective for treating myopia for higher diopter values.